Field of the Invention
The present invention relates to stringed musical instruments having a bridge that is capable of adjusting string pitch.
Background
Modern electric guitars consist principally of a body, a neck and a peghead. The neck extends from the body to the peghead. Most modern guitar strings have a plain, straight end and a “ball end”. The “ball end” is frequently a small metallic cylinder from which the string is wound. Commonly, the plain end of the guitar strings are wound about posts or tuners fixed to the peghead to allow for tuning. The strings run down the neck to body. At the body, the “ball ends” of the strings can be attached to a non-tremolo bridge coupled to the top of the body or the body itself. Non-tremolo type guitar bridges frequently use the ball end of the string to hold the string rigidly to the bridge or pass through the body and are held rigidly into the back of the guitar body. For non-tremolo bridges, the “ball end” of the strings is rigidly fixed in relation to the guitar body.
For tremolo type bridges, the “ball end” of the string is rigidly attached to the bridge plate or cut so that the cut end can be damped rigidly into the bridge. For tremolo type bridges, this bridge plate (or a similar part) is not fixed and can rotate about a pivot point to provide a tremolo effect. The bridge, and hence, the guitar string ends, are not rigidly fixed to the guitar body.
Guitars equipped with a tremolo style bridge allow for changing the pitch of the strings by actuating a tremolo lever extending outward from the bridge, away from the guitar body. Typically, the tremolo lever (commonly known as a tremolo arm or whammy bar) is rigidly fixed to the bridge plate in the plane of the body. The bridge plate is commonly the rigid part of a tremolo bridge to which the saddles and string ends are affixed to. The tremolo lever can be rotated parallel to the bridge plate so that it can be rotated out of the way when not in use. Actuating the tremolo lever towards or away from the guitar body typically rotates the back of the bridge plate into or out of the body about a pivot axis, or fulcrum, at the front of the bridge plate. The pivot axis is perpendicular to the strings when looking at the top of the guitar. This action either stretches or relaxes the strings, thereby increasing or decreasing the pitch of the vibrating strings. Typically, a rigidly attached metallic block extends from the bottom of the bridge plate into a cavity in the body. The cavity in the body is larger than the metallic block and allows for movement of the bridge and block assembly. Two to five tension coil springs are typically fixed to the bottom of this block at one end and the bottom of the guitar body at the other end. The springs are pre-tensioned to pull the block towards the peghead to offset the tension of the strings. String tension can be between 10 to 20 lbf per string, for example. The tension of the springs attached to the bridge block should be adjusted until the bridge plate is relatively parallel to the body when the strings are in tune allowing for an equal range of motion when rotated into or out of the guitar body. These types of tremolos are said to be “floating” because the bridge plate is floating in an equilibrium state between the string and spring tensions against a pivot axis, or fulcrum.
Some players like to rest their hand on the bridge during playing. Additionally, a common technique to diminish the sound of a string is to lightly place the palm on the bridge over the string, commonly referred to as muting. Any force applied to the bridge can disturb the equilibrium of a floating tremolo bridge and cause the guitar to play slightly out of tune. For this reason some tremolo bridges are equipped with various locking mechanisms that, when actuated, can lock the position of the bridge in a neutral position so that the string remains in tune when an external force is applied to the bridge. Some tremolos can lock the position in both directions and some can lock in only one direction, allowing the strings to still decrease in pitch and prevent any change in pitch when a hand is placed on the bridge.
Some characteristics are common to nearly all floating tremolo bridges. actuating the tremolo lever towards the body, when rotated towards the strings, will cause the string pitch to decrease; actuating the tremolo lever away from the body, when rotated towards the string, will cause the pitch to increase; the changes in string length are essentially the same for all the strings of the guitar; all strings are simultaneously affected by actuating the tremolo lever; and the end of the guitar string attached to the bridge rotates with the bridge and is not fixed in relation to the guitar body.
The diameter of the string determines how much the pitch will shift for a given deflection of the tremolo lever. Strings with larger diameter wires, or core wires about which the string is wound will have a larger change in pitch than strings with smaller diameters. For a standard set of electric guitar strings, the low E string can change as much as 5 semitones, while the high E string will shift less than 2 semitones for the same deflection of the tremolo arm. This is due to higher strain in the small diameter strings. For a typical floating tremolo bridge, this means the amount of pitch change for a given deflection of the tremolo lever is not the same for all strings.
Another component that is frequently supplied with a tremolo bridge, specifically Floyd Rose style bridges, is a locking nut. This nut replaces the normal nut at the end of the fingerboard nearest the peghead. The purpose of the locking nut is to eliminate any friction between the nut and string during use of the tremolo. To do this, the string is clamped down so that it cannot move. This prevents the ability to tune the string with the peghead tuners. As a result, many current floating tremolo bridges have “fine tuners” integrated into them to allow for tuning the guitar from the bridge when the string is locked in the nut.